CNT is a well-known nanomaterial. Carbon nanotube, grapheme, 60, diamond are the carbon carbon bond allotropic profiled bodies. In 1991 Sumio lijima found the size of the nanoscale multilayer hollow coaxial carbon nanotubes and published in nature. Due to nanoscale cylindrical structure and unique properties, carbon nanotubes have become promising materials.
For production of the CNTs many methods are known in the art, including arch-discharge and laser ablation method, and Chemical vapour deposition (CVD), CVD is a well-known method for producing of carbon nanotubes. In CVD system, hydrocarbon is used as a precursor. High temperature is required for cracking of catalyst to promote growth of carbon nanotubes. High temperature thermal cracking (800-120° C.) method is used to obtain high purity carbon nanotubes.
The temperature rate can be changed according to the type of hydrocarbon, for example, if acetylene (C2H2) is used over methane (CH4), the growth temperature is reduced. The growth temperature is an influencing parameter for design of a reaction chamber. In addition to the traditional high temperature thermal cracking solution, filament based thermal reactor for rapid growth of carbon nanotube, is also known.
The disadvantages of the commercially available Carbon nanotube growth system are:
1. Quartz tube based system.
2. The processes are costly.
3. Heating and Cooling rate very slow.
4. High process cycle time
5. High power consumption
6. Bigger in size.
Reference is made to U.S. Pat. No. 5,891,251, which discloses a multiple chamber CVD system for a single wafer. A reaction chamber inside a pressure vessel is heated by externally positioned RF induction coils. RF energy from the induction coils passes through the quartz tube to a graphite heating element present inside the reaction chamber. This provides substantially uniform heating by overcoming the problem of non uniform heating due to thickness of deposited layers formed on the walls of the reaction chamber in a CVD process.
Another reference can be made to Patent No. US 2007/003471 A1, wherein the use of functionalized hydrocarbons for CNT synthesis by CVD method is proposed. Hydrocarbon part of the compound acts as carbon source for CNT synthesis and the functional group remove the residual carbon impurities developed during the growth process.
U.S. Pat. No. 5,891,251 entitled ‘CVD REACTOR HAVING HEATED PROCESS CHAMBER WITHIN ISOLATION CHAMBER’ teaches a CVD reactor comprising a pressure chamber for maintaining a reduced pressure environment and a reaction chamber which is contained within and isolates process gas from the pressure chamber. The bell-jar shaped pressure chamber is designed to sustain a low-pressure environment. The parallel plate shaped reaction chamber can optimize the process gas flow. The design prevents deposition of process gases on the walls of the pressure chamber. A wafer is heated by induction coils external to the process chamber, which makes the heat transferred to wafer independent of deposition layers formed on the walls of the reaction chamber.
US Patent Publication No. 2012/220109 A1 entitled ‘PLASMA CVD DEVICE AND METHOD OF MANUFACTURING SILICON THIN FILM’ describes a plasma CVD device comprising a vacuum vessel that contains a discharge electrode plate and a ground electrode plate to which is attached a substrate for thin film formation. The CVD device also has a ground cover at an Interval from the discharge electrode. The discharge electrode and the ground cover has gas inlets and exhaust outlets for process gases. The reference also describes a method for manufacturing silicon thin film using the plasma CVD device. The device also has an electric potential control plate disposed at an Interval from the ground cover.
US Patent Publication No. 2007/0003471 A1 entitled ‘A METHOD OF MANUFACTURING CARBON NANOTUBES’ disclosed a method for manufacturing Carbon Nanotubes, in which carbon nanotubes are grown on a substrate by a chemical vapour deposition process using a reaction gas comprising a compound for carbon source, wherein the compound having a carbon skeleton and a functional group which is effective for removing carbon impurities that deposit during growth of carbon nanotubes, is used as a compound for the carbon source.
US Patent Publication No. 2010/0260933 A1 entitled ‘APPARATUS AND METHOD FOR THE PRODUCTION OF CARBON NANOTUBES ON A CONTINUOUSLY MOVING SUBSTRATE’ describes an apparatus with at least one carbon nanotubes growth zone having a substrate inlet sized to permit a windable length substrate to pass through. A heater is placed in thermal communication with the carbon nanotube growth zone, a feed gas inlet is provided. This apparatus helps in efficient production of carbon nanotubes on a continuously moving substrate.
US Patent Publication no. 2011/0033639 A1 entitled ‘APPARATUS AND PROCESS FOR CARBON NANOTUBE GROWTH’ describes an apparatus for the growth of high aspect ratio emitters or specifically manufacturing carbon nanotubes over a large surface area. The process involves subjecting a substrate to a pressure in the range of 10 to 100 Torr, providing a hydrocarbon gas to be used as source of carbon, heating the hydrocarbon gas by providing radiant heat within a range of 1500-3000 from a heating element which is made of a group consisting of carbon, and conductive ceramics. The apparatus also have a gas distribution element which help in even distribution of gas over the substrate.
US Patent Publication No., 2012/0251432 A1 entitled ‘METHODS FOR THE PRODUCTION OF ALIGNED CARBON NANOTUBES AND NANOSTRUCTURED MATERIAL CONTAINING SAME’ teaches a continuous method for producing a plurality of aligned carbon nanotubes which comprises depositing onto a continuously moving substrate a catalyst to initiate and maintain the growth of carbon nanotubes and a carbon bearing precursor and growing nanotubes inside of a CVD reactor at conditions that promote the growth of substantially aligned carbon nanotubes on the catalyst support material.
US Patent Publication No. 2012/0251433 A1 entitled ‘PROCESS FOR FABRICATING CARBON NANOTUBES AND APPARATUS FOR IMPLEMENTING THE PROCESS’ describes an industrial process for growth of carbon nanotubes (CNTs), comprising synthesis of carbon nanotubes by decomposing a carbon source brought into contact, in a fluidized bed reactor at a reaction temperature between 500-1500° C. with a catalyst I the form of substrate grains covered with a metal, the nanotubes produced being recovered sequentially by discharging them while hot at the reaction temperature for synthesizing the carbon nanotubes.
U.S. Pat. No. 8,257,678 teaches Systems and methods for formation of carbon-based nanostructures. In some embodiments the nanostructures may be formed on a nanopositor. The nanopositor can comprise, in some embodiments at least one of metal atoms in a non-zero oxidation state and metalloid atoms in a non-zero oxidation state. For example, the nanopositor may comprise a metal oxide, a metalloid oxide, a metal chalcogenide, a metalloid chalcogenide, and the like. The carbon-based nanostructures may be grown by exposing the nanopositor, in the presence of absence of a growth substrate, to a set of conditions selected to cause formation of carbon-based nanostructures on the nanopositor. In some embodiments, metal or metalloid atoms in a non-zero oxidation state are not reduced to a zero oxidation state during the formation of the carbon-based nanostructures. In some cases, metal or metalloid atoms in non-zero oxidation state do not form a carbide during the formation of the carbon-based nanostructures.
US 20070110659 discloses an apparatus for producing carbon nanotubes comprising a reaction chamber, a substrate holding member, and a driving member. The holding member is disposed inside the reaction chamber and is configures for holding a substrate for growing carbon nanotubes thereon the driving member is disposed in the reaction chamber and is configured for driving the holding member to move along a direction opposite to the growth direction of the carbon nanotubes in the reaction chamber.
US 20080187648 describes a method and apparatus providing controlled growth and assembly of nanostructures. A first substrate including at least one reaction site is provided. Energy is provided to the reaction site and a reaction species is introduced to the first substrate. A nanostructure is grown from the reaction site. The growth process of the nanostructure is controlled while continuously monitoring the properties of at least one of the nanostructure and the at least one reaction site, and by controlling process variables based on the monitored properties of the nanostructure and the at least one reaction site.